Yuku free message boards

From: Destined For Glory - Dive Bombing, Midway, and the Evolution of Carrier Airpower by Thomas Wildenberg, Naval Institute Press, 1998, ISBN 1-55750-947-6. Chapter 6 - Perfecting the Dive Bomber, starting at the top of page 77 and running into page 80 and referring, time-wise, to the spring and summer of 1930.

"While the Martin company was engaged in preparing the XT5M-1 for the foregoing, a new problem cropped up which threatened to hold up the development of dive bombers. While conducting routine bombing exercises in the fleet, it had suddenly been discovered that under certain circumstances bombs were unexpectedly striking the airplane as they were released. During the previous year a number of accidents had occurred while dive-bombing exercises were being conducted in which airplanes were struck by their own bombs! There were several cases of practice bombs striking the landing gear of F6C-4s and in one instance a miniature bomb struck the propeller. In one extreme instance a live 17-lb. bomb lodged between the wheel and landing-gear strut of an F3B. Miraculously, the pilot managed to land the plane unharmed. Yet another plane landed with a bomb hanging by its arming wire.(27)

"When Rear Adm. Henry V Butler, commander, Aircraft Squadrons, Battle Fleet, learned of these problems he ordered that all planes engaged in practice missions with live bombs be carefully inspected before landing to ensure all bombs had been jettisoned. In cases were bombs failed to be properly released, pilots were to make every effort to discard them into the sea before a landing was attempted. Butler's memo also included a series of instructions spelling out the proper conditions for bombing. No bombs, for example, were to be released while the plane was in a severe skid, nor were they to be dropped from a plane which had been thrown on its back-two actions which had been implicated in the previous accidents.(28)

"The Bureaus of Aeronautics and Ordnance immediately established a joint program to discover a remedy that would remove as many hazards as possible from what was quickly becoming a very dangerous endeavor. The first step was to determine the actual trajectories of the bombs as they were released from various dive angles. An extensive series of drops were soon conducted at the Naval Proving Ground in Dahlgren, Virginia, where motion picture cameras were used to photograph the bombs as they were released from an F7C-1 airplane. The pilot for these flights was Lt. John J. Ballentine, a naval aviator in charge of the aviation detachment at Dahlgren.

"Ballentine's recollections of the events which took place during this period reveal just how little the navy knew about the structural weaknesses of the aircraft it employed for dive bombing and the extreme danger facing the pilots engaged in this activity. At one point the program involved such urgency that Ballentine was required to drop a bomb, land, pick up another, and climb to 10,000 feet without interruption. This heavy schedule sometimes went on all day long.(29)"
. . .
<snipping paragraphs about concurrent aircraft structural failures in F7C-1's not actually related to bomb displacement gear>
. . .
"In the meantime, a trio of engineers that included Lt. Cdr. Arthur C. Miles, head of BuAer's design section, Cdr. C. L. Schuyler, the Inspector of Ordnance at the Naval Proving Ground, and George A. Chadwick, a civilian employee of BuOrd, came up with the idea for a new type of release mechanism that would swing the bomb free of the aircraft structure.(30) The bomb-displacing gear which they invented became the prototype for the bomb "crutch" later used on the SBD Dauntlesses and SB2C Helldivers of World War II fame. It consisted of two arms hinged under the plane with attachment lugs on either side of the bomb. When the bomb was released, the arms forcibly moved the bomb away from the fuselage, ensuring that it would dear the propeller. As the bomb disengaged, a spring-loaded retracting device pulled the arms back into position. It was decided to suspend further testing of the XT5M-1 until such a device could be installed on the new dive bomber.

"Contracts issued by the Bureau of Aeronautics for the construction of aircraft almost always contained some provision with respect to the plane's ordnance requirements, though all gear of this nature (machine guns, sights, bomb racks, flares, and so on) were usually supplied to the contractor. In the case of the XT5M-1 this included the bomb release mechanism, which was to be manufactured and installed by the manufacturer under separate contract from the Bureau of Ordnance.(31)

"By July the Glenn L. Martin Company had produced a detailed blueprint showing the design and installation arrangement of the displacement gear suggested by Lieutenant Commander Miles and company.(32) It took several more months for review and approval, however, before Martin could proceed with fabrication and installation of the new device so that testing of the XT5M-1 could proceed once again.

"In late December 1930, Lt. Cdr. John E. Ostrander Jr. received orders directing him to proceed via air to the Naval Proving Ground at Dahlgren to flight test the special ordnance gear now installed on the Martin plane. Ostrander wrangled the assignment so that Ballentine, who had a wife and child, would not have to test the new mechanism in what was clearly a hazardous undertaking.(33) The two men had become friends while they were both engaged in an earlier assignment at the Naval Proving Ground.

"Final testing was planned for 7 January 1931. Preliminary tests had been conducted the day before using partially loaded practice bombs that Ballentine had dropped in shallow dives. Now Ostrander was scheduled to make a series of drops using fully loaded practice bombs that would culminate in a bomb being released from a near-vertical dive. The first two dives would be made at 45-55 degrees, two more would be made at 60-65 degrees, and another two at 65-70 degrees. If everything worked well, Ostrander would then attempt to make two more drops at 75-80 degrees.(34)

"Fortunately the tests were conducted without incident. The displacement gear worked perfectly and the tests were successfully completed. The Naval Proving Ground was so pleased with the results that Ostrander received a letter of commendation endorsed by both the chief of the Bureau of Ordnance and the chief of the Bureau of Aeronautics. There was even talk within the Bureau of Aeronautics about awarding Ostrander the Distinguished Flying Cross, but this never came to pass.

"The success of the tests conducted by Ostrander was the crowning achievement in BuAer's efforts to develop the first dedicated dive bomber.(35) In April, the XT5M-1 with its wings strengthened and new displacement gear installed was officially accepted by the Board of Inspection and Survey. Moffett immediately ordered the procurement of twelve BM-ls from the Martin company, making them the first airplanes purchased in the new VB category. The production version was nearly identical to the prototype, but had a larger, 625-hp R-1690-44 Pratt and Whitney engine."

Notes:
27. ComAirBatFlt to AirRonsBatFlt, 5 December 1929, BuAer CF File A5-1.
28. Ibid.
29. Ballentine Oral History, 152-53, 155.
30. Pearson, "Dive Bombers," 12.
31. Milburn to INA, 24 July 1928; Chf BuAir to INA, Cleveland, 31 July 1928, BuAer GC File C-8778.
32. See photostat of Martin drawing, BuAer GC File VT5M1 /F41.
33. Ballentine Oral History, 166.
34. Inspector of Ordnance, Naval Proving Ground, Dahlgren, to Chf BuOrd, 24 October 1930, BuAer GC VT5M1 /F41 File.
35. "How about a D.F.C.," handwritten note on routing slip attached to 2nd Endorsement, Chf BuAer to Chf BuNav, 29 January 1931, XT5M-1 File.

And the rest was history.

Rich